Just a point of clarification. This is from the link Meeb provided:
[quote] Until such time as the new legislation comes into effect, adult Australians will continue to lose their Australian Citizenship if they acquire the citizenship of another country. <hr></blockquote>
This applies if an Australian emigrates to, say, the USA and becomes an American citizen. It doesn't apply to those who have dual citizenship by descent, as these people have never "acquired" citizenship of another country, it is their right by birth or patriality.